Conventionally, various techniques relating to wireless communication have been proposed. For example, a technique of performing communication using the Automatic Repeat reQuest (ARQ) scheme has been proposed. In the ARQ scheme, a communication terminal receives a downlink frame from a base station, and when finding an error in data of the downlink frame, requests the base station to retransmit the erroneous data.
A wireless communication technique called WiMAX (Worldwide Interoperability for Microwave Access) is also proposed in which communication is performed based on the OFDMA (Orthogonal Frequency Division Multiple Access) scheme. The WiMAX defines the Hybrid Automatic Repeat reQuest (HARQ) scheme in which the ARQ and an error correction code are combined with each other. For example, as shown in Patent Document 1, a sub-burst which is data used in the HARQ is included in a sub-burst region of a downlink sub-frame transmitted from the base station to the communication terminal.
One of the wireless communication techniques is the Proportional Fairness. In the Proportional Fairness, the priority of transmission to each of communication terminals is set such that the communication terminals can transmit a maximum possible number of bits while the communication quality is still good. This can complete the transmission between the base station and the respective communication terminals within a short time period. Here, fairness among a plurality of communication terminals is maintained by lowering the priority of a communication terminal having a large amount of previous data transmission to thereby allow communication of a communication terminal having a small amount of data transmission.
Patent Document 2 discloses a technique in which a base station according to the WiMAX performs wireless communication with a communication terminal by using the adaptive array antenna scheme.
In the WiMAX, various methods for arranging sub-channels are defined. Among them, a downlink PUSC (Partial Usage of Subchannels) applied to downlink communication defines a plurality of major groups each including a plurality of sub-channels.
In the WiMAX, a downlink burst region for transmitting user data is allocated in a downlink sub-frame used in signal transmission from the base station to the communication terminal. In a case where the base station including an array antenna adopts the downlink PUSC as a method for arranging sub-channels in the downlink burst region and performs beam-forming to control the directivity of the array antenna to thereby transmit a signal to the communication terminal, it is necessary to allocate the downlink burst region to the downlink sub-frame on a major-group basis.
In the WiMAX, on the other hand, it is necessary to allocate the downlink burst region to the downlink sub-frame so as to have a rectangular shape on an OFDM symbol (time)/sub-channel plane whose horizontal axis and vertical axis represent an OFDM symbol and a sub-channel, respectively.
In the WiMAX, furthermore, it is necessary to allocate the downlink burst region to the downlink sub-frame on a so-called “slot” basis.